1. Field of the Invention
This invention generally relates to ligating instruments and more particularly to instruments capable of dispensing ligating bands in a sequential manner.
2. Description of Related Art
It is well known that one can treat various types of lesions including internal hemorrhoids by ligation. The object of ligation is to position an elastic cord, or ligating band, at the lesion to stop circulation through tissue and allow the tissue to die whereupon the body sloughs off the dead tissue.
The following U.S. Pat. Nos. disclose various embodiments of ligating instruments:
3,760,810 (1973) Van Hoorn PA1 4,257,419 (1981) Goltner et al. PA1 4,735,194 (1988) Stiegmann PA1 5,269,789 (1993) Chin et al.
U.S. Pat. No. 3,760,810 to Van Hoorn discloses an instrument for facilitating the placement of a single ligating band or set of bands. The instrument includes, at its distal end, a ligating band dispenser comprising two rigid, concentric tubes. The tubes can slide with respect to each other under the control of a trigger mechanism at the proximal end of the instrument. A rigid endoscope having internal passages forming a suction path and a light path interconnect the trigger mechanism and dispenser. The inner tube can be loaded with a set of one or more elastic rings or ligating bands. A separate stopper bar attaches to the instrument to prevent premature dispensing. When the instrument is located proximate a lesion, a surgeon removes the stopper bar and applies vacuum to draw tissue into a hollow passage at the distal end of the instrument. Pulling on the trigger retracts the inner tube. A radial surface or shoulder on the outer tube engages the ligating band so it can not displace with the inner tube. As the inner tube is withdrawn from the ligating band, it collapses onto the tissue.
U.S. Pat. No. 4,257,419 to Goltner et al discloses a rigid endoscope that includes a ligating band dispenser with an inner tube that moves with respect to an outer tube to dispense a ligating band. This dispenser is oriented at right angles to the rigid endoscope and includes a structure for moving the inner tube of the dispenser in this configuration.
U.S. Pat. No. 4,735,194 to Stiegmann discloses a flexible endoscope ligating instrument in which a flexible endoscope structure includes a biopsy channel and a suction channel extending between the proximal and distal ends. A dispenser, like the dispenser structure shown in the Van Hoorn and Goltner patents, includes an inner tube that moves axially with respect to an outer tube at the distal end of the instrument. The outer tube connects to the distal end of the endoscope. An operating mechanism in the form of a pull wire with a weighted handle maintains tension on the inner tube so it does not displace axially outward while the instrument is being positioned. For some applications it is suggested that the endoscope structure be inserted through an overtube to prevent premature dispensing. Suction can be applied to draw tissue into a central aperture of the dispenser. Then a surgeon pulls the handle and retracts the inner tube axially past the distal end of the outer tube to force the ligating band off the instrument onto the tissue.
Each of the foregoing instruments dispenses a single ligating band or a single set of ligating bands at a single location. None of the patents suggests dispensing ligating bands at discrete locations. The Van Hoorn patent does disclose the possibility of depositing plural ligating bands. However, Van Hoorn seems only to suggest dispensing plural ligating bands at a single site in a single operation. The apparatus disclosed in the Van Hoorn, Goltner or Stiegmann patents apparently would have to rely on a surgeon's sense of touch in order to displace the inner tube by an incremental distance corresponding to the thickness of a stretched ligating band to deposit a plurality of bands at different sites. That would be very difficult to accomplish.
Indeed, when it was desired to deposit ligating bands at different sites, the common practice was to withdraw the entire instrument from the patient and load a new ligating band onto the inner tube. Loading ligating bands on an instrument requires special tools and can be time consuming particularly if the special tooling must be retrieved to install each ligating band individually while the instrument is withdrawn. Each of these instruments requires some structure, such as special stoppers or overtubes, for preventing the premature dispensing of the ligating band. Consequently, none of these instruments is readily adapted for dispensing ligating bands at different sites without withdrawing the instrument after each individual site is ligated.
U.S. Pat. No. 5,269,789 to Chin et al, which is assigned to the same assignee as this invention, discloses a multiple ligating band dispenser for ligating instruments. Interfitted inner and outer structures support a plurality of ligating bands at axially spaced locations. Retraction of the inner structure dispenses one ligating band. Extension of the inner structure advances remaining ligating bands distally and axially so a next retraction dispenses another ligating band. This ligating band dispenser overcomes many, but not all, of the undesirable characteristics of single-band dispensers. For example, prior art single-band dispensers can eject a ligating band inadvertently if, during placement, tissue at the distal end of the dispenser, rather than the physician moves the distal edge of the movable tube. The multiple band dispenser overcomes this problem by using a spring to bias the movable tube to a distal position. However, the use of the spring increases the force that must be used during the dispensing operation. Also, the distal edge of the movable tube is the most distal part of the dispenser. During placement, this edge engages the lesion to form a vacuum seal thereby to allow the lesion to be withdrawn into the lumen of the endoscope. When the movable tube moves proximally during the dispensing operation, the vacuum seal can break thereby enabling the lesion to pull away from the dispenser.